Oilwell drilling operations are conducted through a stack of one or more blowout preventers which are connected to a wellhead member or an extension of a wellhead member. The blowout preventers are necessary to ensure that the drilling contractor will be able to control the well even if a zone of high pressure is penetrated by the drill bit. Occasionally, emergency situations arise where it is necessary to shear the drill pipe and close off the bore of the blowout preventer. To accomplish this, one of the blowout preventers in the stack is equipped with shear rams. Two types of seals have been previously provided for shear rams. The first type includes cross seal packers configured to seal in an essentially vertical plane with the opposing ram, as shown in the K. M. Nicolson U.S. Pat. No. 2,919,111 and the L. E. Williams, Jr. et al. U.S. Pat. No. 3,561,526. The second type of shear ram seals utilizes an essentially horizontal transverse blade seal configured to seal along the shear plane and between the opposing blades, as exemplified in the U.S. Pat. Nos. to A. N. Vujasinovic (3,736,982) and M. J. Meynier III (3,817,326 and 3,946,806).
When the latter type is employed and pipe is sheared, the shearing action tends to force the blades vertically apart and thus increases the gap that must be briged by the horizontal transverse blade seal. In high pressure situations the transverse seal tends to be damaged while attempting to bridge the increased gap.
The F. J. Schweitzer U.S. Pat. No. 2,060,248 and the W. D. Shaffer et al U.S. Pat. No. 2,060,252 both disclose blowout preventer rams that are mortised and tenoned to overlap and limit the upward extrusion of the packing. Neither of these patents suggest the problem mentioned above of sealing in the shearing plane between the blades at high well pressures.